Telephone transmitter



Nov. 1, 1927,. 1,647,244

- C. E. MITCHELL v TELEPHONE TRANSMITTER Filed Nov. 14. 1924 a/ffmr L. Mme

Patented Nov. 1, 1927.

UNITED STATES PATENT OFF IC CLIFFORD E. MITCHELL, OF NEW YORK, N. Y., ASSIGNOR TOWESTERN ELECTRIC M- PANY, INCORPORATED, 013 NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE mamma ian,

Application filed Ijovcmher 14;, 192-1.

This invention relates to telephone transmitters and in articular it relates to an mproved type o microphonic means where n comminuted material such as granular carbon is used as a medium of variable resistance and wherein sound waves are permitted to pass directly through one of the granular carb n u on to ua e a mall diaphr g The object of the invention resides in the 1.0 a ra gem of a ngle-di p gm et ee two granular carbon buttons, one of which is inclosed; between the diaphragm and an open insulating mesh and the other between h di phr gm an a lid lati g d permitting therein a clear path for the sound waves through one of the granular carbon buttons to the diaphragm, This arrangement produces an improvement over the present type ofso-calledj push-pull transmitter.

o this nd, he n ention, 'asapp to the usual cylindrical type" of transmitter button, provides at the point ofentrance for the sound waves a mesh of mercerized silk for retaining the granular carbon in place on one side of the diaphragm, and permitting the sound waves to pass directly to the diaphragm with the least possible resistance. .The invention, therefore, while preserving in general the advantags of construction contained in the art ofthe push-pull type of transmitters, presents an improvement over that construction, first, in that only one diaphragm is used to produce the push-pull a5 efiect; second, that provisions are made for the sound waves to pass in practically a ear p t hr gh on of he g a u r ar bon buttons and to be impinged directly ag ns the d phr gm, nd ast, that the resistance to the voice vibrations is reduced to a minimum,

The invention will be more clearly under stood by reference to the accompanying drawings in which: -15 Fig. 1 shows a vertical sectional view of a transmitter embodying this invention; and

Fig. 2 is a diagrammatic representation of a transmitter circuit showing the connec tions of the resistance varying elements, a single diaphragm between two carbon buttons, an induction coil, a. source of current andv a transmission line.

Referring to the drawing, 1 is a cylindrical metal casing having on one end an internally projecting flangewhose edge is threadser l No. 743.321,

ed to receive and securely hold a transmitter mouthpiece 2 and on the other end a full sized opening to slidablyreceive a unitary embodiment comprising a microphonic means for transmitting the sound waves. The lat ter end of the metal casing is internally threaded for a purposeto be hereinafter ex} p a d" The n y mbod ment is enclosed' in a .drum'3 of insulating material which has its interior surface threaded for the full length to securely mount the various P s pr ng the un e ront; electrode 4 consisting of a metal ring externally threaded to engage the inner surface of the drum 3, 'is set flush with one end of the drum, and across the front of this metal ring is stretched a mesh 5 of mercerized silk, the mesh being held securely in place by a snap ring, 6 arranged in a recess provided in the front of the ring. Against the rear of electrode 4 is placed an insulating annular meme b'er"? whose inside diameter is made considerably less than that of electrode 4, forming thereby a barrler for the purpose of concentrating the voice currents. Adjacent to the insulating member 7 is securely inserted in the drum 3 a second externally-threaded metal ring 8 which serves to holdmember 7 firmly against electrode 4. Ring 8 on its side opposite that adjacent to member 7 is P d d w th a r ce s fo l ng a umber of yh a her-S 9 mad f Paper or u inum fo A diaphr gm l0 havin both sides coated with an insulating material, is loosely support-ed against these washers by a number ot'similar washers 11 and a third externally threaded metal ring 12. The position of the diaphragm provides in front thereof, a chamber 27 which is filled with granular carbon, the filling being accorns plished at the frontjend of the drum 3 when the snap ring 6 and mesh 5 are removed.

The ring'12 at its side opposite that adjacent to the washers is also provided with a recess, which in thiscase is utilized for po sitioning a second insulating annular barrier 13 whose inside diameter is likewise, for the same reason as that of barrier 7 consid'- erably less than those of metal rings e, 8 and 12. The barrier 13is supported inv this position by a metal drum 14 whose outside surface is smooth and inside surfacev is threaded for a purpose hereinafter explained. The end ofthe drum 14, adjacent to the barrier 13, has an internally project;

ing flange for the purpose of supporting an insulating disc 15 which is held firmly in place by a metal plug 16 which is threaded to engage the threaded interior surface of drum 14. At the rear side o1 plug 16 is integrally formed a threaded metal stem 17 over which is fitted a comparatively heavy annular insulating disc 18 drilled at the cen ter to fit snugly around the stem. The drilled insulating disc is securely locked in place by the insulating washer 19, and metal washer 20 and nut 21. The whole unit formed by the drum 14 and disc 18 is securely held in position by means of another externally threaded metal ring 22 similar in size to the other metal rings, and this ring is recessed to receive the outside edge of the disc 18 for positioning and holding the disc in place. The provision of this so-called unit serves in the capacity of a removable insulated stopper for the chamber 28, at the rear of the diaphragm 10, which like chamber 27 is also filled with granular carbon. This so-called unit is securely locked in place by the metal clamping ring 22 which is also externally threaded to engage the drum 3. The unitary embodiment comprising the insulative drum 3 is now locked in position by two metal rings 24 and 25 the latter being externally threaded to engage the threaded portion of the inside surface of the metal casing 1.

The metal casing is electrically connected with the metal ring 4 and serves as a front electrode connected to one end of the primary winding of the induction coil 60 in the transmitter circuit a diagram of which is shown in Fig. 2, the so-called unit comprising the drum 14 and the drilled insulating disc 18 provides a second electrode which is connected to the other end otthe primary winding of the induction coil, and the adjacent rings 22 and 23 are brought into contact with the adjacent rings 8 and 12 by means of the spring member 26, and the four rings combined provide a third electrode which is connected to a source of current.

In Fig. 2, which shows the diagram of the transmitter circuit, the electrodes 52 and 53, which correspond to 4 and-17, respectively, and their respectively associated carbon buttons in chambers 27 and 28, shown in Fig. 1, are connected by means of conductors 50 and 51 to the extremities of the primary winding 57 of the induction coil 60, the secondary winding 61 being connected to the line by conductors 58 and 59. The movable electrode 54 corresponding to the electrode comprising rings 8 and 12 in Fig. 1, is common to both 52 and 53 and is connected to the middle point of the primary winding through the local battery 56.

The operation of the transmitter circuit is as 'fOllOWSI The normal current flow is in opposite directions through the primary, the core of the coil remaining neutral. One operation of the diaphragm 10 and its associated electrode 54 causes current to rise in one half of the primary and simultaneously to fall in the other half, and, as these effects are opposite, the resultant action on the secondary produces a strong rise in one direction through the whole length of the secondary equal to the sum of the individual eftects. On the reverse oscillation, the current in the secondary first falls to zero and then reverses to an equal degree.

Referring now to Fig. 1, a sound wave impressed upon the diaphragm 10, causing a movement of the diaphragm toward the rear will compress the granules inthe carbon button in chamber 28 and cause an expansion between the granules in the carbon button in chamber 27, producing thereby'a push-pull effect. This will decrease the re sistance in the circuit shown in Fig. 2, comprising conductor 51 and cause an increase in the flow of current therethrough, and at the same time, the resistance in the circuit including conductor 50 will be increased, causing a corresponding decrease in the current flowing therethrough. Thus the total efiect of these current changes in these circuits as heretofore stated, are additive so tar as the magnetic energization of the core in the induction coil 60 is concerned.

What is claimed is:

1. In a telephone transmitter, a unitary structure arranged to form a chamber, a resistance varying material in said chamber, a vibratory diaphragm separating said chamber into front and rear compartments, one of which is arranged to permit voice waves to pass through the resistance varying material of the front compartment and be impinged directly against said diaphragm.

2. In a telephone transmitter the combination of an insulating internally threaded sleeve, a plurality of externally threaded annular electrodes engaged therein and spaced apart, a plurality of annular insulating barriers between said electrodes the inner diameters of said barriers being less than those of the said electrodes to efiect a concentration of voice current passing therethrough, a vibratory diaphragm in said chamber arranged to form therein two yieldable transmitter buttons, means for closing both ends of said sleeve to form a chamber, the means closing the front chamber being a silk mesh to permit the sound waves to pass through the granules of the first button and impinge directly on said diaphragm.

3. In a telephone transmitter, the combination of a mouth-piece support, a unitary embodiment comprising an insulating sleeve, a plurality of annular metal rings mounted therein, a plurality of annular insulating rings mounted between said metal rings to form three separate electrodes, insulating means for closing both ends of said sleeve to form a chamber one of said means consisting of a piece of silk fabric held in place over the opening by a snap ring, yieldable carbon buttons and a vibratory diaphragm in said chamber, said diaphragm arranged to separate said buttons, and means for removably mounting said embodiment in said support.

4. In a telephone transmitter the combination comprising an insulating internallythreaded sleeve, three stationary annular electrodes mounted and spaced apart in said sleeve, insulating rings located between concentrically mounted With respect thereto,

and arranged to effect a concentration of currents passing through said electrodes,

of said sleeve to form a chamber, carbon granules therein, a single vibratory diaphragm arranged in said chamber to evenly divide said granules into two parts providing thereby two carbon transmitter buttons one of which permits the direct passage of the sound Waves to the diaphragm.

In Witness whereof, I hereunto subscribe my name this 3rd'day of November, A. D., 1924.

CLIFFORD E. MITCHELL. 

